A motor drive device used in a conventional electronic component mounting apparatus, as shown in FIG. 12, consists of an NC unit 21 for command generation (hereinafter called a master), servo driver units 22, 28, and 29 (hereinafter called slaves), and cables 30 and 31 for connecting the master and slaves to carry out serial communication. The master 21 is provided with a master side communication section 35 which communicates with the slaves 22, 28, and 29. The slaves 22, 28, and 29 are each composed of a slave side communication section 23 which carries out the serial communication with the master 21 via the cable 30 or 31, a servo operation controller 24 which drives each servo motor 26, and a power source 25. The servo motor 26 has an encoder 27 for detecting its rotational position, and a detection signal is fed back to the controller 24.
In the above configuration, the master 21 issues operation commands for the motors 26 to the slaves 22, 28, and 29 at predetermined intervals, and the commands are transmitted to the slave side communication sections 23 of the slaves 22, 28, and 29 via the cables 30 and 31, respectively. The servo operation controller 24 and the power source 25 control the motor 26 based on the received commands from the master 21 in such a way as to satisfy the commands.
By the way, a recent electronic component mounting apparatus required to move at high speed and with high accuracy, for example, has the encoder 27 with high resolution for precisely detecting a position of the motor 26, so that a lot of command information has to be transmitted in the serial communication. Taking a case of the encoder 27 or a linear scale, for example, resolution thereof was previously 10,000 pulses per count, but recently it multiplies 10 to 100-fold, so that an amount of the transmitted command information accordingly increases. Also increase in the number of axes of the servo motor 26, according to extension of functions of the electronic component mounting apparatus, brings about accelerating increase in the number of sensors such as an origin point sensor and a limit sensor needed for drive axes, so that it becomes impossible to sufficiently transmit information because of lack of communication capacity in the conventional serial communication.
Since an amount of information transmitted in the serial communication increases with increase in the number of slaves connected to the master, if the number of the slaves increases in response to a demand of increase in the number of axes and the like, there is a problem in which an interval of transmission to each slave is increased and servo function of each slave is degraded.
Increase in an amount of transmitted information per unit time, that is, increase in transmission speed of the information can solve this problem. However, in this case the conventional motor drive device cannot be used because it is necessary to change all driver units to those of a high speed type. Also it is economically inadvisable to equally use the high speed type driver units as a driver unit of a relatively low speed motor, such as the motor for driving a conveyor section in which a substrate is transferred to a position to mount a component, and as a driver unit of a relatively high speed motor, such as the motor for driving a transfer head which sucks the component supplied by a component feeding section and moves over the substrate to mount the component.
Accordingly, as shown in FIG. 12, in a case where there are a plurality of communication formats having different transmission speed and data formats without compatibility (two communication formats are mixed as slaves A and B have a communication format A and a slave C has a communication format B), each of the plurality of communication formats A and B needs to have an individual serial communication section, so that there are problems in which a load of the master 21 becomes heavy and an amount of wiring increases.
In light of the foregoing problems, a main object of the present invention is to provide a motor drive device with high degree of compatibility which deals with a new communication format with a lot of information on a single serial bus in addition to enabling controlling of a conventional device.